Enzymes

Question 1

Describe cofactors

Answer 1

non-protein component needed for activity

Question 2

Describe coenzymes

Answer 2

Complex organic molecule, usually formed from vitamins

Question 3

Describe prosthetic groups

Answer 3

Cofactor covalently bound to the enzyme or very tightly associated with the enzyme

Question 4

Describe apoenzymes

Answer 4

The protein component of an enzyme containing a prosthetic group

Question 5

Give three ways in which enzymes catalyse reactions

Answer 5

• increase rate of spontaneous reactions
• lower the activation energy of biochemical reactions
• accelerate movement toward reaction equilibria

Question 6

Define the Michaelis Constant

Answer 6

Km = 1/2 Vmax = k.1 + k2/k1

Question 7

Larger Km values indicate

Answer 7

a less stable ES complex

Question 8

Lower Km values indicate

Answer 8

a more stable ES complex

Question 9

Km tells us about

Answer 9

the affinity of the enzyme for the substrate

Question 10

Describe competitive inhibition

Answer 10

• these inhibitors bind to enzymes in the same way as the intended substrate
• bind non-covalently and tend to resemble proper substrate
• leads to increase in Km as affinity for proper substrate decreases
• increasing conc. of substrate can displace the competitor and Vmax can be achieved

Question 11

Describe non-competitive inhibition

Answer 11

• these inhibitors bind non-covalently
• bind to a site other than the active site of the enzyme
• enzyme can still bind to active site so Km is unchanged
• inhibitor cannot be displaced by increasing conc. of substrate so Vmax will decrease

Question 12

Metabolites can bind to allosteric sites on some enzymes to act as

Answer 12

inhibitors or activators

- this is an example of non-competitive inhibition

Question 13

Describe the concerted model

Answer 13

• each subunit can exist in 2 different confirmations
• one will have low Km, other will have high Km
• with no substrate, enzyme flips between conformations
• all units must be the same conformation i.e. in concert
• when 1 substrate binds it holds enzyme in open conformation
• increases affinity and explains sigmoid curve

Question 14

Describe the sequential model

Answer 14

• no flipping between different conformational states
• binding causes a conformation change in 1 subunit
• this causes a change in another subunit making further binding easier
• binding sensitises the enzyme to more substrate